This application claims priority under 35 USC §119 or §365 to Great Britain Patent Application No. 1401689.3 entitled “Audio Signal Processing” filed Jan. 31, 2014 by Karsten Vandborg Sorensen the disclosure of which is incorporate in its entirety.
Audio signal processing refers to the intentional altering of an audio signal to achieve a desired effect. It may occur in the analogue domain, digital domain or a combination of both and may be implemented, for instance, by a generic processor running audio processing code, specialized processors such as digital signal processors having architectures tailored to such processing, or dedicated audio signal processing hardware. For example, audio captured by a microphone of a user device may be processed prior to and/or following transmission over a communication network as part of a voice or video call.
An audio signal may be processed by an audio processing chain comprising a plurality of audio signal processing components (hardware and/or software) connected in series; that is whereby each component of the chain applies a particular type of audio signal processing (such as gain, dynamic range compression, echo cancellation etc.) to an input signal and supplies that processed signal to the next component in the chain for further processing, other than the first and last components which receive as an input an initial analogue audio signal (e.g. a substantially unprocessed or ‘raw’ audio signal as captured from a microphone or similar) and supply a final output of the chain (e.g. for supplying to a loudspeaker for play-out or communication network for transmission) respectively. Thus variations in processing by one component in the chain can cause variations in the output of subsequent components in the chain.
One type of audio processing component that may be used in such a chain is a noise suppression component. The audio signal may comprise a desired audio component but also an undesired noise component; the noise suppression component aims to suppress the undesired noise component whilst retaining the desired audio component. For instance, an audio signal captured by a microphone of a user device may capture a user's speech in a room, which constitutes the desired component in this instance. However, it may also capture undesired background noise originating from, say, cooling fans, environmental systems, background music etc.; it may also capture undesired signals originating from a loudspeaker of the user device for example received from another user device via a communication network during a call with another user conducted using a communication client application, or being output by other applications executed on the user device such as media applications—these various undesired signals can all contribute to the undesired noise component of the audio signal.